I didn't say in your case it wasn't the box!
In my case, I could just be driving down the road, and all of a sudden my truck would pull hard to the right, nearly striking the curb! No matter how hard I'd fiht it, it would shoot to the right. My box had about 1/4 turn of play. First I replaced the pump. Then the centerlink since it had play. The drag link because it had play. The only thing left was the box, right? WRONG. I decided to replace the ball joints next, because changing the box didn't solve my problem. Since the truck pulled to the right, I started on the right side. Guess what? I found my problem, and it wasn't the ball joints!
As it turned out.... the axle U joint was siezed. Well 2 of the trunion bearings were. So just driving along, centrifugal force would cause it to rotate, and when the siezed up part was aligned just right, it would cause the truck to pull hard right. Had I bought the truck in the winter, I would have found out about the U joint sooner. Being I bought it in Sept. I was just getting it ready for plowing. I checked the 4wd when I bought it, but didn't go around making sharp turns in 4wd on dry pavement. I drove it in a straight line to be sure the 4wd worked, and that the t case shifter worked, and all gears could be reached.
Oh yeah, the trunion bearings were siezed due to RUST. The good news is, since Sept 1995, all I have had to replace is that leaky reman. box. Well, that and an axle shaft I snapped while plowing during the blizzard of 96. We got 30" of snow, and all my accounts were plowed, so I can't complain.